Ferrite Magnetic Powder for Bond Magnet and Manufacturing Method of the Same, and Bond Magnet

ABSTRACT

To provide ferrite magnetic powders for bond magnet capable of surely suppressing residual hexavalent chrome, being an environmental load substance, having no adverse influence on the magnetic characteristics, which is an obstacle in use, and without damaging productivity and at a low cost. The method includes the steps of obtaining sintered powders by sintering raw material powders; wet-pulverizing the sintered powders; wet-cleaning the sintered powders; and annealing the cleaned sintered powders, wherein in the step of the wet-pulverization and in the step of wet-cleaning, generation of the hexavalent chrome, being an environmental load substance, is suppressed by performing the pulverization and cleaning while maintaining pH of a dispersion solvent at 8.5 or less, at the time of pulverization and cleaning.

TECHNICAL FIELD

The present invention relates to ferrite magnetic powder for bond magnetcontaining iron and an alkaline earth metal as composite elements and amanufacturing method of the same, and a bond magnet using a magneticcomponent of this ferrite magnetic powder.

DESCRIPTION OF RELATED ART

A bond magnet is a compound permanent magnet obtained by compactingmagnetic powders by a binder such as rubber and resin, with thismagnetic (hard magnetic body) powder set as a filler, having advantagessuch as a high free degree of shape and a proof against fracture inmechanical characteristics, and having further advantages such as easymass production by mold molding and excellent productivity.

Therefore, there are significantly wide-ranging application products ofthe bond magnet, which are widely utilized, for example, in a doorpacking of a refrigerator, each kind of magnet sheet, a spindle motor ofperipheral equipment of a personal computer, each kind of meter ofautomobile, healthcare equipment, stationary, toys, etc.

Usually, ferrite magnetic powder having excellent residual magnetic fluxdensity and intrinsic coercive force is used as the magnetic powder,being the filler of this bond magnet. Various kinds of ferrite magneticpowders for bond magnet have been developed as described in patentdocuments 1 and 2.

A ferrite magnetic material includes iron and an alkaline earth metal ascomposite elements in many cases, and the same thing can be said for thecase of the ferrite magnetic powder for bond magnet. BaO.Fe₂O andSrO.6Fe₂O₃, etc, are given as examples of this kind of ferrite magneticmaterial, and these materials are also used as the ferrite magneticpowder for bond magnet.

This ferrite magnetic powder for bond magnet is manufactured through thefollowing steps.

-   (1) The step of obtaining sintered powder by sintering raw material    powders containing the iron and alkaline earth metal.-   (2) The step of pulverizing the sintered powders obtained in the    step (1).-   (3) The step of cleaning the sintered powders pulverized in the step    (2).-   (4) The step of annealing the cleaned sintered powders in the step    (3).    Patent document 1: Publication of U.S. Pat. No. 3,257,936    Patent document 1: Japanese Patent Laid Open Publication No.    2003-86412

DISCLOSURE OF THE INVENTION Problem to be Solve by the Invention

In recent years, there is a severe request to electric/electronicproducts, such as a request to characteristics capable of coping withits purpose of use and in addition a request to the cost. Further, inrecent years, from the viewpoint of an environmental problem, a productwith small environmental load is desired.

Inventors of the present invention consider it industrially importantthat magnetic characteristic close to a sintered isotropic magnet isexhibited by the bond magnet which is widely used in variouselectric/electronic products. Therefore, the inventors of the presentinvention study on the invention of the bond magnet having the magneticcharacteristic close to the sintered isotropic magnet. Then, as a resultof the study, the inventors of the present invention achieve a techniqueof improving the magnetic characteristic of the bond magnet, bycontaining small amount of Cr (chrome) in the bond magnet. This isbecause when a moderate amount of Cr is contained in the ferritemagnetic powder, being the raw material of the bond magnet,dispersibility is improved, and flowability at the time of mixing theferrite magnetic powder, binder resin, and rubber is improved. Also,this is because when the flowability is improved, as a result,orientation of the ferrite magnetic powder is increased, and themagnetic characteristic is improved in the manufactured bond magnet.

However, hexavalent chrome, being an environmental load substance, issometimes detected in the manufactured bond magnet. However, thehexavalent chrome of an amount below environmental criteria is remainedin the bond magnet, there is nothing to be concerned about environmentalcontamination immediately. However, as described above, the bond magnetis utilized in significantly various kinds of and large amount ofelectric/electronic products. Therefore, the inventors of the presentinvention consider it necessary to reduce the amount of the hexavalentchrome, being the environmental load substance, as much as possible,without deteriorating the magnetic characteristic of the bond magnet.

Under such a circumstance, the present invention is provided, and anobject of the present invention is to provide ferrite magnetic powdercapable of manufacturing bond magnet having high characteristic, becausethe flowability is high at the time of mixing with the binder resin andbinder rubber, and capable of reducing hexavalent chrome to a detectionlimit or less, in the manufactured bond magnet.

Means to Solve the Problem

The inventors of the present invention study on a cause of detecting thehexavalent chrome for bond magnet, and the following points areclarified.

As described above, the manufacturing step of the ferrite magneticpowders for manufacturing a bond magnet includes at least one of thestep of cleaning the sintered powders containing suitable amount of Crelement obtained by sintering the raw material powders, and the step ofwet-pulverizing the sintered powders. The cleaning step and thewet-pulverizing step are generally performed, by using water as asolvent (dispersion solvent).

By adding the wet cleaning step, in the manufactured ferrite magneticpowders, non-reacted impurity components are eluted into the solvent andremoved. Then, when the annealing process is performed thereafter,coagulation among particles and grain growth are tremendouslysuppressed. Therefore, by adding heat in this annealing process, astrain in crystal generated during pulverization is removed, thusrecovering the magnetic characteristic and maintaining thedispersibility among particles in the ferrite magnetic powderscontaining a suitable amount of Cr element. Accordingly, when mixed withnatural rubber, resin, and rubbers, being binders, the ferrite magneticpowders are uniformly dispersed into these binders, thus improvingflowability and orientation of the ferrite magnetic powders in thismixed material. As a result, in the step thereafter, when injectionmolding of the mixed material is performed in a magnetic field, anindividual ferrite magnetic powder particle is further uniformlyoriented, and therefore magnetic force is improved in the manufacturedbond magnet.

In addition, by performing the step of wet-pulverizing, non-reactedimpurity components in the ferrite magnetic powder particles are elutedinto the solvent and removed, and it becomes possible to efficientlypulverize the non-reacted impurity components. As a result, thenon-reacted impurity components can be pulverized with goodproductivity, up to an optimal particle size, in terms of the magneticcharacteristic and also in terms of the flowability, when mixed withresin.

However, in these wet cleaning step and wet pulverizing step, alkalineearth metals such as non-reacted Sr and Da that exist in the sinteredpowders are eluted into water, being the dispersion solvent, thusincreasing pH of this dispersion solvent to 8.5 or greater. Then, a partof the Cr compound contained in the sintered powders is set in a stateeasily changed to the hexavalent chrome, and it is found that a part ofthe Cr compound is changed to the hexavalent chrome when sintered in theannealing step thereafter.

Here, in the wet cleaning time and the wet pulverizing time, theinventors of the present invention achieves a structure of suppressingthe Cr compound from being changed to the hexavalent chrome bymaintaining hydrogen ion concentration of the used dispersion solvent ina range of pH 8.5 or smaller not allowing the Cr compound to elute, andcompletes the present invention.

Namely, a first means for solving the aforementioned problem providesferrite magnetic powders, being the ferrite magnetic powders for bondmagnet containing iron and alkaline earth metal, which has undergone wetcleaning and/or wet pulverizing process, containing Cr element of 100ppm or more and 3000 ppm or less, and having no hexavalent chromedetected therein.

A second means provides ferrite magnetic powders, being the ferritemagnetic powders for bond magnet containing iron and alkaline earthmetal, which has undergone wet cleaning and/or wet pulverizing,containing Cr element of 100 ppm or more and 3000 ppm or less, with acontent of the hexavalent chrome set at 1 ppm or less.

A third means provides the ferrite magnetic powders according to thefirst or the second means, wherein in the magnetic characteristics of acompact prepared by adding 0.4 cc of polyester resin to 7 g of theferrite magnetic powders, which is then packed into a mold of φ15 mm,and pressure of 8 MPa is added thereto, residual magnetic flux densityBr is 1730 Gauss or greater and intrinsic coercive force iHc is 2270 Oeor greater.

A fourth means provides a manufacturing method of ferrite magneticpowders for manufacturing the ferrite magnetic powders for bond magnetfrom raw material powders containing iron and alkaline earth metal,including the steps of:

obtaining sintered powders by sintering the raw material powders;

wet-cleaning the sintered powders; and

annealing the wet-cleaned sintered powders,

wherein in the step of wet-cleaning, cleaning is performed, with pH of adispersion solvent used in cleaning set at 8.5 or less.

A fifth means provides a manufacturing method of ferrite magneticpowders for manufacturing the ferrite magnetic powders for bond magnetfrom raw material powders containing iron and alkaline earth metal,including the steps of:

obtaining sintered powders by sintering the raw material powders;

pulverizing the sintered powders;

wet-cleaning the pulverized sintered powders; and

annealing the wet-cleaned sintered powders,

wherein in the wet-cleaning step, cleaning is performed, with pH of adispersion solvent used in cleaning is set at 8.5 or less.

A sixth means provides a manufacturing method of ferrite magneticpowders for manufacturing the ferrite magnetic powders for bond magnetfrom raw material powders containing iron and alkaline earth metal,including the steps of;

obtaining sintered powders by sintering the raw material powders;

wet-pulverizing the sintered powders; and

annealing the wet-pulverized sintered powders,

wherein in the wet-pulverizing step, wet-pulverization is performed,with pH of a dispersion solvent used in the wet-pulverization set at 8.5or less.

A seventh means provides the manufacturing method of the ferritemagnetic powders for bond magnet according to any one of the fourth tosixth means, wherein in the step after the step of obtaining thesintered powders and before the step of annealing the sintered powders,a compound having a boiling point of 200° C. or more containing carbonas an indispensable element and one or more kinds of elements selectedfrom H, 0, N, Cl, is added to the sintered powders.

An eighth means provides the manufacturing method of the ferritemagnetic powders for bond magnet according to any one of the fourth tosixth means, wherein in the step after the step of obtaining thesintered powders and before the step of annealing the sintered powders,divalent Fe and/or a compound containing the divalent Fe is added to thesintered powders.

A ninth means provides the manufacturing method of the ferrite magneticpowders according to any one of the fourth to sixth means, wherein thewet-pulverized and/or wet-cleaned sintered powders are subjected toreduction treatment in a gas atmosphere in a temperature range of 80° C.to 300° C., containing at least one kind or more of H₂ gas, CO gas, NOgas, and HC(hydrocarbon) gas.

A tenth means provides a bond magnet containing the ferrite magneticpowders for the bond magnet according to any one of the first to thirdmeans.

ADVANTAGES OF THE INVENTION

According to the ferrite magnetic powders of the present invention, theflowability of the ferrite magnetic powders when mixed with binder resinand binder rubber can be secured. Further, an amount of the hexavalentchrome in the manufactured bond magnet can be set at a detection limitor less.

BEST MODE FOR CARRYING OUT THE INVENTION

The ferrite magnetic powders according to the present invention containCr element of 100 ppm or more and 3000 ppm or less. However, content ofthe hexavalent chrome is 1 ppm or less, being a detection limit of thediphenylcarbazide spectrophotometric method.

Namely, the ferrite magnetic powders according to the present inventioncontains the Cr element of 100 ppm or more and 3000 ppm or less, andtherefore when mixed with resin, a melt flow rate (MFR) is set high tobe 70 g/10 min or more. Then, since this MFR is set high, mixture of theferrite magnetic powders and resin proceeds smoothly, thus realizing amixture having high uniformity. The bond magnet manufactured byperforming an injection molding of the compact which is manufacturedfrom the mixture having high uniformity in a magnetic field exhibitshigh magnetic' characteristic. Incidentally, in order to measure themagnetic characteristics of the ferrite magnetic powders according tothe present invention, 0.4 cc of polyester resin is added to 7 g of theferrite magnetic powders, then the mixture is compacted into a die ofφ15 mm, and pressure of 9 MPa is added thereto and the mixture isthereby molded, to produce a compact, and the magnetic characteristicsof the ferrite magnetic powders is measured. Then, it is found that thiscompact has values of 1730 Gauss or more as a residual magnetic fluxdensity Br, and 2270 Oe or more as an intrinsic coercive force iHc.

Then, when the bond magnet is manufactured by performing injectionmolding in the magnetic field, by using the ferrite magnetic powdersshowing 1730 Gauss or more of residual magnetic flux density Br, 2270 Oeor more of intrinsic coercive force iHc in the case of being compacted,it is found that the magnetic characteristic such as BHmax of 1.8 MGOeor more close to a sintered isotropic magnet is exhibited by theobtained bond magnet, and therefore this bond magnet can be widelyapplied to a motor and a magnetic roll, etc.

Meanwhile, although the ferrite magnetic powders according to thepresent invention contains the Cr element of 100 ppm or less and 3000ppm or more, the content of the hexavalent chrome, being anenvironmental load substance, can be set at 1 ppm or less, being thedetection limit or less of the diphenylcarbazide spectrophotometricmethod. The content of this hexavalent chrome is far less amount thanthe environmental criteria (such as 1000 ppm defined by ROHS reference).

First Embodiment

Next, regarding a manufacturing method of ferrite magnetic powders forbond magnet according to the present invention, a preferable embodimentof this manufacturing process will be explained, with reference to FIG.1.

As shown in a flow of FIG. 1, the manufacturing step of the ferritemagnetic powders according to the present invention includes the stepssuch as

(1) blending and mixing step

(2) granulation step

(3) sintering step

(4) pulverizing step

(5) cleaning step

(6) annealing step.

Each step will be explained hereunder.

(1) Blending/Mixing Step:

Strontium carbonate and iron oxide are weighed and mixed to be fall in arange of SrCO₃:Fe₂O₃=1:5.20 to 6.00 at a molar ratio, to obtain amixture.

At this time, the iron oxide with a purity of 99.0 to 99.9%, andcontaining 100 ppm or more and 3000 ppm or less of Cr element is used.This is because by setting the content of Cr at 100 ppm or more, aneffect of increasing dispersibility of the ferrite magnetic powders isexhibited, and by setting the content of Cr at 3000 ppm or less,deterioration of the magnetic characteristics of the ferrite magneticpowders can be avoided.

(2) Granulation Step:

Water of 5 to 15 wt % is added and mixed into the obtained mixture, andthe mixture is granulated in a spherical shape of φ3 to 10 mm, to obtaingranulated powders.

(3) Sintering Step:

The granulated powders obtained in the granulating step are dried andthereafter sintered in a time range from 10 minutes to 2 hours and in atemperature range from 900° C. to 1350° C. in an electric furnace, toobtain sintered powders. Here, when a sintering temperature is set at900° C. or more, ferrite forming reaction proceeds. Meanwhile, when thesintering temperature is set at 1350° C. or less, coarse growth ofcrystal grains and sintering among crystals can be avoided in thesintered powders. In addition, when the sintering time is set at 10minutes or more, the effect of this sintering can be obtained.Meanwhile, from the viewpoint of productivity, the sintering time ispreferably set to be 2 hours or less.

(4) Pulverizing Step:

In the pulverizing step, the sintered powders obtained in the sinteringstep are wet-pulverized, so that its average particle size becomes 2.5μm or less. This wet-pulverization is performed, by using water as adispersion solvent. However, at this time, an acid compound is added tothe solvent, so as to maintain pH of the dispersion solvent to be 8.5 orless. A so-called pH control is performed, and by a wet-pulverizationunder this pH control, the ferrite magnetic powders are manufactured.

(5) Cleaning Step:

In the cleaning step, water is added to sintered powders of slurry shapeobtained in the pulverizing step to dewater the sintered powders, byadding water of 0.1 wt. fold, with pH of 5 to 8 with respect to theamount of the sintered powders excluding the solvent. Alternately, afterdewatering the sintered powders of slurry shape obtained in thepulverizing step, the sintered powders excluding the solvent is cleanedby using the water of 0.1 wt. fold, with pH of 5 to 8 with respect tothe amount of the sintered powders, and is dried in a drier of 80 to150° C.

(6) Annealing Step:

The annealing step is performed for removing crystal distortiongenerated in the crystal of the ferrite magnetic powders at the time ofpulverizing of the sintered powders or at the time of breaking thesintered powders after drying. It is preferable to set the annealingtemperature at 850° C. to 1050° C.

This is because by setting the temperature of this annealing step at850° C. or more, the crystal distortion is removed to make it possibleto further enhance iHc. Meanwhile, when this annealing temperature isset at 1050° C. or less, generation of cohesive ferrite magnetic powerscan be suppressed, and dispersibility of the ferrite magnetic powderscan be maintained. Then, the ferrite magnetic powders according to thepresent invention can be obtained after this annealing step.

In the aforementioned ferrite magnetic powders, when the content of thehexavalent chrome is measured by a diphenylcarbazide spectrophotometricmethod, it is confirmed to be a detection limit or less, therefore 1 ppmor less.

Then, the bond magnet is manufactured by a normal method, using theaforementioned ferrite magnetic powders. It is confirmed that this bondmagnet can be used for the purpose of use of each kind ofelectric/electronic appliance, without trouble.

Second Embodiment

Next, regarding a manufacturing method of the ferrite magnetic powdersfor carbon according to the present invention, a preferred embodimentwith different manufacturing process will be explained.

The manufacturing step of the ferrite magnetic powders according to thepresent invention includes each step of: (1) blending and mixing step,(2) granulating step, (3) sintering step, (4) pulverizing step, (5)cleaning step, and (6) annealing step.

Each step will be explained hereunder.

(1) Blending/Mixing Step:

Strontium carbonate and iron oxide are weighed and mixed to satisfy arange of SrCO₃:Fe₂O₃=1:5.20 to 6.00 at a molar ratio, to obtain themixture.

At this time, the iron oxide with 99.0 to 99.9% of purity of Fe₂O₃, and100 ppm-3000 ppm of content of Cr element, is used. This is because bysetting the content of Cr at 100 ppm or more, effect of enhancingdispersibility of the ferrite magnetic powders is exhibited, and bysetting the content of Cr at 3000 ppm or less, deterioration of themagnetic characteristics of the ferrite magnetic powders can be avoided.

(2) Granulating Step:

By adding and mixing the water of 5 to 15 wt % into the obtainedmixture, the mixture is granulated into a spherical shape of φ3 to 10mm, to obtain granulated powders.

(3) Sintering Step:

After drying the granulated powders obtained in the granulating step,the granulated powders are sintered in an electric furnace at atemperature range from 900° to 1350° C., for 10 minutes to 2 hours, toobtain the sintered powders. Here, by setting the sintering temperatureat 900° C. or more, a ferrite formation reaction proceeds. Meanwhile, bysetting the sintering temperature at 1350° C. or less, coarse growth ofcrystal grains and sintering among particles can be avoided. By settingthe sintering time at 10 minutes or more, the effect of this sinteringcan be obtained. Meanwhile, from the viewpoint of productivity, thesintering time is preferably set at 2 hours or less.

(4) Pulverizing Step:

In the pulverizing step, the sintered powders obtained in the sinteringstep are subjected to wet-pulverizing process until its average particlesize reaches 2.5 μm or less. By setting the average particle size of thesintered particles at 2.5 μm or less, the magnetic characteristics suchas a coercive force is improved in the manufactured bond magnet.

This wet-pulverization is performed by making the water a dispersionsolvent, and at this time, an acidic compound is added to the solvent soas to maintain pH of the solvent at 8.5 or less, to perform a so-calledpH control. Then, by the pulverization under this pH control, theferrite magnetic powders are manufactured.

Further preferably, in this pulverizing step, water is used as thedispersion solvent, and particles having average particle size of 100 μmor less such as carbon, or a compound containing carbon as an essentialcomponent, and containing one or more kinds of elements selected from H,0, N, Cl having a boiling point of 200° C. or more (abbreviated simplyas carbon compound hereunder in some cases), or both of the carbon andthe carbon compound are added and mixed into the sintered powdersobtained in the sintering step. Then, this mixture is wet-pulverized, toset the average particle size of a ferrite magnetic powder simple bodyat 2.5 μm or less.

At this time, added amount of carbon and/or carbon compound is set at0.2 wt % to 2.0 wt % with respect to the sintered powders.

Further, preferably carbon and/or carbon compound is added and mixed inthe form of powders having an average particle size of 100 μm or less,or in the form of liquid. This is because by taking this form, theeffect of reducing the hexavalent chrome slightly remained in theferrite magnetic powders is enhanced. Here, alcohols having a boilingpoint of 200° C. or more (diethylene glycol, triethyleneglycol,diethanol amine, triethanolamine, dipropyleneglycol, tripropyleneglycol,polyvinyl alcohol (PVA), etc) are given as examples of the compoundhaving the boiling point of 200° C. or more containing carbon as anessential component and containing one or more kinds of elementsselected from H, O, N, Cl.

Here, when this carbon compound has a particle form like PVA, etc, thiscarbon compound may be dissolved into the solvent such as water andalcohol once. In addition, by setting the added amount of this carbonand carbon compound at 0.2 wt % or more of the ferrite magnetic powders,a sufficient reduction effect is exhibited. Further, by setting thisadded amount at 5 wt % or less with respect to the ferrite magneticpowders, it is possible to avoid a circumstance such as reducing theferrite magnetic powders to ferrite or generating sintering betweenferrite particles. Accordingly, if the added amount of this carbon andcarbon compound is set at 0.2 wt % or more and 5 wt % or less withrespect to the ferrite magnetic powders, it is possible to obtain theferrite magnetic powders whereby the bond magnet with highcharacteristics can be manufactured.

(5) Cleaning Step:

In the cleaning step, by adding water of 0.1 wt. fold, with pH of 5 to 8with respect to the amount of the sintered powders excluding thesolvent, to the sintered powders of slurry shape obtained in thepulverizing step, to dewater the sintered powders. Alternately, afterdewatering the sintered powders of slurry shape obtained in thepulverizing step, by adding water of ≧0.1 wt. fold, with pH of 5 to 8with respect to the amount of the sintered powders excluding thesolvent, the sintered powders is cleaned and dried in a drier of 80 to150° C.

Note that it is also possible to perform in this cleaning step addingand mixing operation of particles of an average particle size of 100 μmor less explained in the aforementioned (4) pulverizing step, such ascarbon or carbon compound, or both of the carbon and carbon compound.

(6) Annealing Step:

The annealing step is performed to remove the crystal distortiongenerated in the crystal of the ferrite magnetic powders, at a time ofpulverizing the sintered powders or at a time of breaking the sinteredpowders after drying. Further, when the carbon and/or carbon compound isadded in the pulverizing step or the cleaning step in addition toremoving this crystal distortion, the slightly remained hexavalentchrome is reduced and removed by a reduction effect of the added carbonand/or carbon compound. The annealing temperature is preferably set atin a range from 850° C. to 1050° C.

By setting the temperature of this annealing step at 850° C. or more,the crystal distortion is removed and iHc can be enhanced in themanufactured bond magnet. Further, when the carbon and/or carboncompound is added in the pulverizing step or the cleaning step inaddition to removing this crystal distortion, even in a case where thehexavalent chrome slightly remains, it is reduced and removed.Meanwhile, by setting the annealing temperature at 1050° C. or less,generation of the cohesion of the ferrite magnetic powders issuppressed, and the dispersibility of the ferrite magnetic powders canbe maintained. As a result, the ferrite magnetic powders according tothe present invention can be obtained after the annealing step.

In addition, it is also preferable that in the (5) cleaning step,bivalent Fe, or a compound containing bivalent Fe (such as FeO, FeSO₄,FeCl₂), or both of the bivalent Fe and the compound containing thebivalent Fe, are converted to an amount of bivalent Fe, and 0.2 wt % to2 wt % of which is added to the sintered powders.

Even in a case of adding the bivalent Fe and/or the compound containingthe bivalent Fe, the hexavalent chrome is reduced and removed by areduction force of this bivalent Fe, in the same way as a case of addingthe carbon and/or carbon compound, thus making it possible to obtain theferrite magnetic powders of the present invention.

When the content of the hexavalent chrome in the ferrite magneticpowders is measured by the diphenyl carbazide spectrophotometric method,it is confirmed that the content of the hexavalent chrome is 1 ppm orless, being the detection limit or less of the diphenylcarbazidespectrophotometric method.

Then, the bond magnet is manufactured by a normal method, using theaforementioned ferrite magnetic powders. It is confirmed that this bondmagnet can be used for the purpose of use of each kind ofelectric/electronic appliance, without trouble.

Third Embodiment

Next, further another preferable embodiment of the manufacturing processof the manufacturing method of the ferrite magnetic powders for carbonaccording to the present invention.

The manufacturing steps of the ferrite magnetic powders according to thepresent invention includes each kind of step of (1) blending and mixingstep, (2), granulating step, (3) sintering step, (4) pulverizing step,(5) cleaning step, and (6) annealing step.

Each step will be explained hereunder.

(1) Blending/Mixing Step:

Strontium carbonate and iron oxide are weighed and mixed to be fall in arange of SrCO₃:Fe₂O₃=1:5.20 to 6.00 at a molar ratio, to obtain amixture.

At this time, the iron oxide with a purity of 99.0 to 99.9%, andcontaining 100 ppm or more and 3000 ppm or less of Cr element is used.This is because by setting the content of Cr at 100 ppm or more, aneffect of increasing dispersibility of the ferrite magnetic powders isexhibited, and by setting the content of Cr at 3000 ppm or less,dispersibility of the ferrite magnetic powders can be enhanced, withoutdeteriorating the magnetic characteristics of the manufacture bondmagnet.

(2) Granulating Step:

5 to 15 wt % water is added and mixed into the obtained mixture, whichis then granulated into a spherical shape of φ3 to 10 mm, to obtaingranulated powders.

(3) Sintering Step:

After drying the granulated powders obtained in the granulating step,the granulated powders are sintered in the electric furnace at atemperature in a range from 900° C. to 1350° C. for 10 minutes-2 hours,to obtain the sintered powders. Here, by setting the sinteringtemperature at 900° C. or more, the ferrite forming reaction proceeds.Meanwhile, when the sintering temperature is set at 1350° C. or less,coarse growth of crystal grains and sintering among crystals can beavoided in the sintered powders. In addition, when the sintering time isset at 10 minutes or more, the effect of this sintering can be obtained.Meanwhile, from the viewpoint of productivity, the sintering time ispreferably set to be 2 hours or less.

(4) Pulverizing Step:

In the pulverizing step, water is added to the sintered powders obtainedin the sintering step as the dispersion solvent, and the sinteredpowders obtained in the sintering step are wet-pulverized, so that itsaverage particle size becomes 2.5 μm or less. By performing thiswet-pulverizing, the ferrite powders of high characteristics can bemanufactured, in a state of fine particles, with good productivity.

Note that it is possible to perform in this pulverizing step theoperation of adding and mixing the carbon of average particle size of100 μm or less, and/or the carbon compound explained in the pulverizingstep (first embodiment (4)).

(5) Cleaning Step:

In the cleaning step, water is added to sintered powders of slurry shapeobtained in the pulverizing step to dewater the sintered powders, byadding water of ≧0.1 wt. fold, with pH of 5 to 8 with respect to theamount of the sintered powders excluding the solvent. Alternately, afterdewatering the sintered powders of slurry shape obtained in thepulverizing step, the sintered powders excluding the solvent is cleanedby using the water of Z 0.1 wt. fold, with pH of 5 to 8 with respect tothe amount of the sintered powders, and is dried in a drier of 80 to150° C.

Note that the operation of adding and mixing the carbon of averageparticle size of 100 μm or less and/or carbon compound explained in thepulverizing step of the (first embodiment (4)) may be performed in thiscleaning step.

(6) Annealing Step:

The annealing step is performed for removing crystal distortiongenerated in the crystal of the ferrite magnetic powders at the time ofpulverizing of the sintered powders or at the time of breaking thesintered powders after drying. Further, when the carbon and/or carboncompound is added in the pulverizing step or the cleaning step inaddition to removing the crystal distortion, even in a case where thehexavalent chrome slightly remains, it is reduced and removed.

Preferably, the annealing temperature is set in a range from 850° C. to1050° C.

This is because by setting the temperature of the annealing step at 850°C. or more, the aforementioned crystal distortion is removed and iHc canbe enhanced in the manufactured bond magnet. Meanwhile, this is becauseif the annealing temperature is set at 1050° C. or less, the generationof the cohesion of the ferrite magnetic powders can be suppressed andthe dispersibility of the ferrite magnetic powders can be maintained.

Next, the ferrite magnetic powders after the annealing step are placedin a constant temperature bath that can be air-tightly closed, equippedwith a stirring function, and inside of this bath is replaced withreductive gas containing one or more kinds of gases selected from H₂gas, CO gas, NO gas, HC (hydrocarbon) gas, to set the temperature insideof the bath in a range from 80° C. to 300° C. Whereby, the hexavalentchrome is subjected to reduction process.

Here, concentration of the reductive gas is preferably set at 0.01% ormore. By setting the concentration of the reductive gas at 0.01% ormore, effect of reducing and removing the remained hexavalent chrome isincreased, thereby making it possible to reduce the time required forthe reduction process to 12 hours or less.

Further, if the processing temperature is set at 80° C. or more, theeffect of reducing the hexavalent chrome is exhibited, and if theprocessing temperature is set at 300° C. or less, the ferrite isreduced, thereby making it possible to avoid the deterioration of themagnetic characteristics of the ferrite in the manufactured bond magnet.

Then, the ferrite magnetic powders according to the present inventionare obtained after this annealing step.

In addition, it is also preferable that in the (4) pulverizing step, (5)cleaning step, instead of the carbon and/or carbon compound, bivalentFe, or a compound containing bivalent Fe (such as FeO, FeSO₄, FeCl₂), orboth of the bivalent Fe and the compound containing the bivalent Fe, areconverted to an amount of bivalent Fe, and 0.2 wt % to 2 wt % of whichis added to the sintered powders.

Even in a case of adding the bivalent Fe and/or the compound containingthe bivalent Fe, the hexavalent chrome is reduced and removed by areduction force of this bivalent Fe, in the same way as a case of addingthe carbon and/or carbon compound, thus making it possible to obtain theferrite magnetic powders of the present invention.

When the content of the hexavalent chrome in the ferrite magneticpowders is measured by the diphenylcarbazide spectrophotometric method,it is confirmed that the content of the hexavalent chrome is 1 ppm orless, being the detection limit or less of the diphenylcarbazidespectrophotometric method.

Then, when flowability is obtained based on a measurement method of amelt flow rate (MFR) as will be described later, it is found that theferrite magnetic powders according to the present invention haveexcellent flowability and can be easily and uniformly mixed with resinand rubber. By compressively molding this mixture, the bond magnetaccording to the present invention can be manufactured. Also, it isconfirmed that this bond magnet can be used for the purpose of use ofeach kind of electric/electronic product, without trouble.

Characteristics as a green compact of a ferrite magnetic powderaccording to the present invention are as follows: the value of residualmagnetic flux density Br is 1730 Gauss or more, and the value ofintrinsic coercive force iHc is 2270 Oe, and further as the magneticcharacteristic of the bond magnet at the time of conducting a magneticfield orientation, BHmax shows 1.8 MGOe or more, and therefore theferrite magnetic powders of the present invention corresponds to asintered isotropic magnet.

EXAMPLES

The present invention will be more specifically explained hereunder,with reference to the drawings. However, the present invention is notlimited to the scope of these examples.

Example 1

Strontium carbonate and iron oxide were weighed and mixed to be fall ina range of SrCO₃:Fe₂O₃=1:5.75 at a molar ratio. Then, this weighedsubstance was mixed by a sample mill, to obtain a mixed powder. Next, byadding 10 wt % of water to this mixed powder, which was then kneaded, togranulate this kneaded substance, which was then dried as a granulatedpowder having an average particle size of 8 mm. This dried granulatedpowder was set in the electric furnace, and sintered at 1200° C. in anatmospheric air for 2 hours, to obtain a sintered substance. Thissintered substance was coarsely pulverized by the sample mill, to obtaina sintered powder having an average particle size of 13.5 μm.

Next, this sintered powder was wet-pulverized for 120 minutes by usingan attriter with a volume of 10 L. First, 1.3 kg of the sinteredpowders, 15 g of hydrochloric acid with concentration of 35%, and 10 kgof steel ball of φ8 mm were weighed. Next, while operating the attriterat a rotation speed of 200 rpm, 10 kg of the steel ball, 2 L of waterwith pH 6.7, 15 g of the hydrochloric acid, and 1.3 kg of the sinteredpowders were charged into this attriter in this order, to obtain slurry.At this time, the slurry was batched off and left at rest. Then, pH of asupernatant solution was measured, to obtain pH of 1.25. Meanwhile, theattriter was continued to operate for 120 minutes, to performwet-pulverization. Then, the slurry was batched and left at rest again,and pH of the supernatant solution was measured. Then it is found thatpH after elapse of 60 minutes shows 5.29, and pH after elapse of 120minutes shows 7.7, and this reveals that pH gradually rises, along withelapse of wet-pulverizing time. However, pH of the slurry during thiswet-pulverization is maintained to 8.5 or less.

When the wet-pulverization was completed, the slurry obtained by usingfilter paper and infundibulum was dewatered, and thereafter was decantedand cleaned by water of 4 L with pH 6.5. The sintered powders obtainedby cleaning and filtering were dried in the drier of 120° C., to obtainstrontium ferrite powder having average particle size of 1.47 μm.

Next, this strontium ferrite powder was set in the electric furnace,which was then annealed for 20 minutes at 980° C. under the atmosphericair, and the ferrite magnetic powder for bond magnet according toexample 1 was manufactured.

When powder characteristics of the manufactured ferrite magnetic powderfor bond magnet according to the example 1 were measured, a specificsurface area diameter measured by an air-permeation method was 1.65 μmand compaction density was 3.29 g/cm³. Note that a mode of a measurementmethod such as the specific surface area diameter, etc, will bedescribed later.

In addition, the melt flow rate (MFR) is 71.5 g/10 min, showing highflowability.

Next, by using the ferrite magnetic powder for bond magnet according tothe example 1, a green compact according to the example 1 wasmanufactured.

When the magnetic characteristics of the green compact according to theexample 1 was measured, Br was 1870 Gauss (described as simply Ghereafter in some cases) and iHc was 2570 Oe, showing high values.

Next, when measurement of the magnetic characteristics of the ferritemagnetic powder for bond magnet according to the example 1 was performedby “5. measurement of the magnetic characteristics of an injectionmolded body”, Br was 2751 G, iHc was 2444 Oe, BHmax was 1.84 MGOe, andSQx was 0.972.

As described above, it is found that the flowability of the ferritemagnetic powder for bond magnet according to the example 1 is excellent,and therefore SQx value, being one of indicators of orientation in aninjection molded body according to the example 1, is also high, andfurther this ferrite magnetic powder for bond magnet has a high magneticcharacteristic.

In addition, when the amount of the hexavalent chrome of the ferritemagnetic powders for bond magnet according to the example 1 was measuredby the diphenylcarbazide spectrophotometric method (a method ofextraction was executed by 3% solute method of a low quality method.),it was found that the value was 1 ppm or less, being the detection limitor less.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to the example1, and measured values of the magnetic characteristics were described intable 1.

Here, a specific mode will be explained, for the measurement method ofthe specific surface area, etc, of the ferrite magnetic powders for bondmagnet according to the example 1.

1. Measurement of the Specific Surface Area Diameter by Air-PermeationMethod

A powder specific surface area measuring apparatus SS-100 by SHIMADZUCORP. was used as a measuring apparatus.

By using a press machine attached to this powder specific surface areameasuring apparatus, a sample of the ferrite magnetic powders for bondmagnet was press-molded to be formed in a sectional area of 2 cm² andthickness of 1 cm. Meanwhile, a small amount of Vaseline was applied ona sample tube of this powder specific surface area measuring apparatus,and the press-molded ferrite powder sample for bond magnet was set inthis sample tube.

Then, time t was measured, at which 2 cm³ of air is transmitted throughthis press-molded ferrite powder sample for bond magnet, and from thismeasured time t, the specific surface area of the ferrite powder samplefor bond magnet was calculated by using the following conversionformula.

Sw=(14/ρ)·((ΔP·A·t·ε ³)/(η·L·Q·(1−ε)²))^(0.5)

However, Sw indicates the specific surface area. ρ indicates the densityof the press-molded ferrite powder sample for bond magnet, and in thisexample, this value is 5.1 g/cm³. AP indicates a pressure difference,and in this example, this value is 40 g/cm². A indicates a sectionalarea of a sample layer, and in this example, this value is 2 cm². ηindicates a viscosity coefficient, and in this example, this value is180×10−6 g/cm². L indicates the thickness of a sample, and in thisexample, this value is 1 cm. W indicates a weight of the sample, and inthis example, this value is 5 g. Q indicates a transmission amount ofair, and in this example, this value is 2 cm³. t indicates a requiredtime for transmission. ε indicates a void content (1−W/(ρ·A·L)) of thesample layer.

Next, on the basis that the particle of the ferrite powder sample forbond magnet is formed in a cube and the particles are uniform, thespecific surface area was calculated from the specific surface areadiameter: Da=6/(ρ·Sw).

2. Measurement of Pressed Density

The value of the pressed density was obtained by measuring a densityvalue after pressurizing and molding the ferrite powder sample for bondmagnet with a pressure of 1 ton/cm².

3. Measurement of Melt Flow Rate (MFR)

(1) 3-lots of the ferrite magnetic powders for bond magnet weremanufactured, and 3000 g of ferrite magnetic powders for bond magnet waspicked from each lot. Meanwhile, 30 g of silane-coupling agent (byNippon Unicar Company Limited, Product name A-1122), 15 g of water, and30 g of methanol were prepared. They were filled in a high speed mixer(by FUKAE KOUGYOU KK, FS-GC-5JI), and were mixed for 5 minutes ofprocessing time at 8 m/sec of peripheral speed, to obtain a mixture.

(2) The obtained mixture wad dried for 100° C.×90 minutes to obtaindried powders.

(3) The obtained 3030 g of dried powders and 400 g of 6-nilon (by USEIndustries, LTD, P-1010) were filled in the high speed mixer (by FUKAEKOUGYOU KK, FS-GC-5JI), and mixed for 5 minutes of processing time at 8m/sec of peripheral speed, to obtain a mixture.

(4) The obtained mixture was kneaded, to obtain a pellet having 2 mm ofaverage diameter. Note that in this kneading, a continuous kneadingexclusion type device (KCK70-22VEX (6)) by KCK LTD, was used.

(5) 10 kg of load was applied on the obtained pellet at 270° C., and theweight of the kneaded product excluded from a flowability evaluationdevice within 10 minutes was measured, and this value was set as a meltflow rate (MFR). Note that the flowability evaluation device, C-5059D2,by TOY( )SEIKI KK was used in measurement. This device was constitutedbased on 1YIS-K7210.

4. Measurement of the Magnetic Characteristic of the Green Compact

First, the green Compact was manufactured from the ferrite magneticpowders for bond magnet.

-   -   7 g of the ferrite magnetic powders for bond magnet was weighed,        and 0.4 cc of polyester resin was added and mixed therein.    -   The weighed ferrite magnetic powders for bond magnet were filled        in a metallic mold formed in a columnar shape of φ15 mm, then        pressurized by pressure 8 MPa for 20 seconds to obtain the green        compact.    -   The obtained green compact was pulled out of the metallic mold,        then put in the drier, and dried for 30 seconds at 150° C. Then,        after the temperature was cooled down to 25° C., being the room        temperature, Br and iHc of this columnar green compact were        measured by a BH tracer (by TOEI KOGYO KK, BH tracer).

5. Measurement of the Magnetic Characteristics of the Injection MoldedBody

The magnetic characteristics of the injection molded body were measuredas follows.

-   -   (1) In the same way as (1) to (4) explained in the        aforementioned “3. Measurement of melt flow rate (MFR)”, the        pellet with average diameter of approximately 2 mm was obtained.    -   (2) The obtained pellet was injection-molded by 8.5N/mm² molding        pressure at temperature of 290° C., in a magnetic field of 10K        Oe, by using an injection molding machine, to obtain a columnar        molded product with diameter 15 mm×height 8 mm.    -    Note that in this columnar molded product, a direction of the        orientation of the magnetic field was set as a direction along a        central axis of a column.    -   (3) Br, iHc, BHmax, SQ×(Br/4πI) of the obtained columnar molded        product was measured by the BH tracer (by TOEI KOGYO KK, BH        tracer).

Example 2

By performing the same operation using the same raw material as that ofthe example 1, the sintered powders were manufactured. The manufacturedsintered powders were subjected to wet pulverizing step as describedbelow, and strontium ferrite powders according to example 2 weremanufactured.

First, 1.3 kg of sintered powders and 10 kg of steel ball of φ8 mm wereweighed. Next, while operating the attriter at a rotation speed of 200rpm, 10 kg of the steel ball and 2 L of water with pH6.7 were chargedinto this attriter. Further, a steel pipe with diameter of 0.6 mm wasinserted to this aqueous solution, and carbon dioxide gas was blownthereinto for 20 minutes at a speed of 1 mL/min. When this aqueoussolution was left at rest and pH measurement was performed, the valuewas pH4.80. Next, 1.3 kg of the sintered powders were charged into thisaqueous solution while operating the attriter at a rotation speed of 200rpm, and the slurry was obtained. This slurry was batched off and leftat rest. Then, pH of a supernatant solution was measured, to obtain pHof 6.64.

Next, the wet-type pulverization was performed by rotating the attriterfor 120 minutes, while the carbon dioxide gas was continued to be blownin. The slurry was batched and left at rest again, after 60 minutes inthe middle of this wet-type pulverization and after 120 minutes from theend of the wet-pulverization, and when pH of the supernatant solutionwas measured, pH after 60 minutes was 5.80, and pH after 120 minutes was5.7, and pH of the slurry during performing the wet-type pulverizationwas maintained to be lower than 8.5.

When the wet-type pulverization was completed, in the same way as theexample 1, after dewatering the slurry, decantation was performed to drythe sintered powders obtained by cleaning and filtering, and strontiumferrite powders with average particle size of 1.42 μm was obtained.

Next, this strontium ferrite powders were set in the electric furnace,and subjected to annealing for 20 minutes at 980° C. in the atmosphericair, to manufacture the ferrite magnetic powders for bond magnetaccording to example 2.

When the powder characteristics of the ferrite magnetic powders for bondmagnet according to the example 2 were measured in the same way as theexample 1, the specific surface area diameter measured by theair-permeation method was 1.71 μm and the pressed density was 3.31g/cm³.

Also, the melt flow rate (MFR) was 72.8 g/10 min, being highflowability.

In the same way as the example 1, the green compact was manufacturedfrom the ferrite magnetic powders for bond magnet according to theexample 2. Then, when the magnetic characteristics of this green compactwere measured, Br was 1870 Gauss (called G hereafter), and iHc was 2560Oe, being high values.

Further, in the same way as the example 1, a kneaded product accordingto the example 2 was manufactured form the ferrite magnetic powders forbond magnet according to the example 2.

When measuring the magnetic characteristics of the injection molded bodyobtained by injection-molding the kneaded product according to theexample 1 in the magnetic field, Br was 2757 G, iHc was 2440 Oe, BHmaxwas 1.85 MGOe, and SQx was 0.971.

As described above, it is found that the flowability of the ferritemagnetic powder for bond magnet according to the example 2 is excellent,and therefore SQx value, being one of indicators of orientation in aninjection molded body according to the example 2, is also high, andfurther this ferrite magnetic powder for bond magnet has a high magneticcharacteristic.

In addition, in the same way as the example 1, when measuring the amountof the hexavalent chrome of the ferrite magnetic powders for bond magnetaccording to the example 2, it was found that the value was 1 ppm orless, being the detection limit or less.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to the example2, and measured values of the magnetic characteristics were described intable 1.

Example 3

The sintered powders were manufactured by performing the same operationas that of the example 1 using the same raw materials.

Strontium ferrite powders were manufactured by performing the sameoperation for the manufactured sintered powders in the wet-typepulverizing step as the operation of the example 1, excluding the pointthat hydrochloric acid and carbon corresponding to 0.5 wt % of thesintered powders were added.

Specifically, 1.3 kg of the sintered powders, 12 g of the hydrochloricacid with concentration of 35%, and 0.65 of carbon with average particlesize of 3 μm, and 10 kg of steel ball of +8 mm were weighed. Next, whileoperating the attriter at a rotation speed of 200 rpm, 10 kg of thesteel ball, 2 L of water with pH6.7, 15 g of the hydrochloric acid, and1.3 kg of the sintered powders were charged into this attriter in thisorder, to obtain slurry.

At this time, the slurry was batched off and left at rest. Then, pH of asupernatant solution was measured, to obtain pH of 1.32. Meanwhile, theattriter was continued to operate for 120 minutes, to performwet-pulverization. Then, the slurry was batched and left at rest again,and pH of the supernatant solution was measured. Then it is found thatpH after elapse of 60 minutes shows 5.81, and pH after elapse of 120minutes shows 8.2, and this reveals that pH gradually rises, along withelapse of wet-pulverizing time. However, pH of the slurry during thiswet-pulverization is maintained to 8.5 or less.

When the wet-pulverization was completed, in the same way as the example1, after dewatering and filtering the slurry, decantation was performed,thereby drying the sintered powders obtained by cleaning and filtering,and the strontium ferrite powders with average particle size of 1.50 μmwas obtained.

Next, the strontium ferrite powders were set in the electric furnace,then subjected to annealing for 20 minutes at 980° C. in the atmosphericair, and the ferrite magnetic powders for bond magnet according toembodiment 3 was manufactured.

When measuring the powder characteristics of the ferrite magneticpowders for bond magnet according to the example 3 in the same way asthe example 1, the specific surface area diameter measured by theair-permeation method was 1.95 μm and the pressed density was 3.43g/cm³.

Also, the melt flow rate (MFR) was 77.8 g/10 min, being highflowability.

In the same way as the example 1, the green compact was manufacturedfrom the ferrite magnetic powders for bond magnet according to theexample 3. Then, when the magnetic characteristics of this green compactwere measured, Br was 1880 G, and iHc was 2570 Oe, being high values.

Further, in the same way as the example 1, the kneaded product accordingto the example 3 was manufactured from the ferrite magnetic powders forbond magnet according to the example 3.

When measuring the magnetic characteristics of the injection molded bodyobtained by injection-molding the kneaded product according to theexample 3 in the magnetic field, Br was 2780 G, iHc was 2400 Oe, BHmaxwas 1.84 MGOe, and SQx was 0.980.

As described above, it was found that the flowability of the ferritemagnetic powder for bond magnet according to the example 3 wasexcellent, and therefore SQx value, being one of indicators oforientation in an injection molded body according to the example 3, wasalso high, and further this ferrite magnetic powder for bond magnet hada high magnetic characteristic.

In addition, when the amount of the hexavalent chrome of the ferritemagnetic powders for bond magnet according to the example 3 was measuredin the same way as the example 1, it was found that the value was 1 ppmor less, being the detection limit or less.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to the example3, and measured values of the magnetic characteristics were described intable 1.

Example 4

The sintered powders were manufactured by performing the same operationusing the same raw materials as those of the example 1.

The strontium ferrite powders were manufactured by operating themanufactured sintered powders in the same way as the example 1 excludingthe point that hydrochloric acid was not added in the wet-typepulverizing step.

Specifically, 1.3 kg of the sintered powders, 12 g of the hydrochloricacid with concentration of 35%, and 10 kg of steel ball of 48 mm wereweighed. Next, while operating the attriter at a rotation speed of 200rpm, 10 kg of the steel ball, 2 L of water with pH6.7, 15 g of thehydrochloric acid, and 1.3 kg of the sintered powders were charged intothis attriter in this order, to obtain slurry. At this time, the slurrywas batched off and left at rest. Then, pH of a supernatant solution wasmeasured, to obtain pH of 1.38. Meanwhile, the attriter was continued tooperate for 120 minutes, to perform wet-pulverization. Then, the slurrywas batched and left at rest again, and pH of the supernatant solutionwas measured. Then it is found that pH after elapse of 60 minutes shows5.90, and pH after elapse of 120 minutes shows 8.4 and this reveals thatpH gradually rises, along with elapse of wet-pulverizing time. However,pH of the slurry during this wet-pulverization is maintained to 8.5 orless.

When the wet-pulverization was completed, in the same way as the example1, after dewatering and filtering the slurry, decantation was performed,thereby drying the sintered powders obtained by cleaning and filtering,and the strontium ferrite powders with average particle size diameter of1.50 μm was obtained.

Next, this strontium ferrite powders were set in the electric furnace,and subjected to annealing for 20 minutes at 980° C. in the atmosphericair.

Then, the annealed strontium ferrite particles were set in theair-tightly closed constant temperature bath having a stirring function,and the mixed gas (set hydrogen gas concentration at 0.1%) of nitrogenand hydrogen was flown in this constant temperature bath at a flow rateof 1 L/min, to replace the atmosphere in this constant temperature bathwith the mixed gas. Then, after this replacement was completed, anatmosphere temperature in this constant temperature bath was increasedup to 150° C. while stirring the annealed strontium ferrite powders andthis state was maintained for 2 hours, and thereafter the temperaturewas decreased down to the room temperature. Thus, the ferrite magneticpowders for bond magnet according to example 4 were manufactured.

When measuring the particle characteristics of the ferrite magneticpowders for bond magnet according to the example 4 in the same way asthe example 1, the specific surface area measured by the air-permeationmethod was 1.90 μm, and the pressed density was 3.41 g/cm³.

Also, the melt flow rate (MFR) was 75, 5 g/10 min, being highflowability.

In the same way as the example 1, the green compact was manufacturedfrom the ferrite magnetic powders for bond magnet according to theexample 4. Then, when the magnetic characteristics of the green compactwere measured, Br was 1880 G, and iHc was 2550 Oe, being high values.

Further, in the same way as the example 1, the kneaded product accordingto example 4 was manufactured from the ferrite magnetic powers for bondmagnet according to the example 4.

When measuring the magnetic characteristics of the injection molded bodyobtained by injection-molding the kneaded product according to theexample 4 in the magnetic field, Br was 2760 G, iHc was 2433 Oe, BHmaxwas 1.86 MGOe, and SQx was 0.978.

As described above, it is found that the flowability of the ferritemagnetic powder for bond magnet according to the example 2 is excellent,and therefore SQx value, being one of indicators of orientation in aninjection molded body according to the example 4, is also high, andfurther this ferrite magnetic powder for bond magnet has a high magneticcharacteristic.

In addition, in the same way as the example 1, when measuring the amountof the hexavalent chrome of the ferrite magnetic powders for bond magnetaccording to the example 4, it was found that the value was 1 ppm orless, being the detection limit or less.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to the example4, and measured values of the magnetic characteristics were described intable 1.

Comparative Example 1

The sintered powders were manufactured by performing the same operationusing the same raw materials as those of the example 1.

In the same way as the example 1, the strontium ferrite powders weremanufactured from the manufactured sintered powders, excluding the pointthat the hydrochloric acid was not added in the wet-type pulverizingstep.

Specifically, 1.3 kg of the sintered powders, and 10 kg of steel ball ofφ8 mm were weighed. Next, while operating the attriter having a volumeof 10 L at a rotation speed of 200 rpm, 10 kg of the steel ball, 2 L ofwater with pH6.7, and 1.3 kg of the sintered powders were charged intothis attriter in this order, to obtain slurry. At this time, the slurrywas batched off and left at rest. Then, pH of a supernatant solution wasmeasured, to obtain pH of 9.95. Meanwhile, the attriter was continued tooperate for 120 minutes, to perform wet-pulverization. Then, the slurrywas batched off and left at rest again, and pH of the Supernatantsolution was measured. Then it is found that pH after elapse of 60minutes shows 11.1, and pH after elapse of 120 minutes shows 11.9 andthis reveals that pH gradually rises, along with elapse ofwet-pulverizing time. Then, the value of the pH of the slurry duringthis wet-pulverization becomes higher than pH 8.5 at which Cr isconsidered to be changed to the hexavalent chrome.

When the wet-type pulverization was completed, in the same way as theexample 1, after dewatering and filtering the slurry, decantation wasperformed, thereby drying the sintered powders obtained by cleaning andfiltering, and the strontium ferrite powders with average particle sizediameter of 1.50 μm were obtained.

Next, this strontium ferrite powders were set in the electric furnace,and subjected to annealing for 20 minutes at 980° C., in the atmosphericair, and the ferrite magnetic powders for bond magnet according tocomparative example 1 were manufactured.

When measuring the powder characteristics of the ferrite magneticpowders for bond magnet according to the comparative example 1 in thesame way as the example 1, the specific surface area measured by theair-permeation method was 1.80 μm, and the pressed density was 3.39g/cm³.

Also, the melt flow rate (MFR) was 72.3 g/10 min, being highflowability.

The green compact was manufactured from the ferrite magnetic powders forbond magnet according to the comparative example 1, in the same way asthe example 1. Then, when the magnetic characteristics of this greencompact were measured, Br was 1870 G, and iHc was 2560 Oe, being highvalues.

Further, the kneaded product according to the comparative example 1 wasmanufactured from the ferrite magnetic powders for bond magnet accordingto the comparative example 1 in the same way as the example 1.

When measuring the magnetic characteristics of the injection molded bodyobtained by injection-molding the kneaded product according to thecomparative example 1 in the magnetic field, Br was 2753 G, iHc was 2442Oe, BHmax was 1.84 MGOe, and SQx was 0.972.

As described above, it is found that the flowability of the ferritemagnetic powder for bond magnet according to the comparative example 1is excellent, and therefore SQx value, being one of indicators oforientation in an injection molded body according to the example 2, isalso high, and further this ferrite magnetic powder for bond magnet hasa high magnetic characteristic.

However, when the amount of the hexavalent chrome of the ferritemagnetic powders for bond magnet according to the comparative example 1was measured in the same way as the example 1, it was found that thevalue was 49 ppm.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to thecomparative example 1, and measured values of the magneticcharacteristics were described in table 1.

Comparative Example 2

The sintered powders were manufactured by performing the same operationas that of the example 1, excluding the point that the iron oxidecontaining 5 ppm of Cr element was used as the raw material.

The strontium ferrite powders were manufactured from the manufacturedsintered powders, in the same way as the example 1, excluding the pointthat the hydrochloric acid was not added in the wet-type pulverizingstep.

Specifically, 1.3 kg of the sintered powders, and 10 kg of steel ball ofφ8 mm were weighed. Next, while operating the attriter having a volumeof 10 L at a rotation speed of 200 rpm, 10 kg of the steel ball, 2 L ofwater with pH6.7, and 1.3 kg of the sintered powders were charged intothis attriter in this order, to obtain slurry. At this time, the slurrywas batched off and left at rest. Then, pH of a supernatant solution wasmeasured, to obtain pH of 9.95. Meanwhile, the attriter was continued tooperate for 120 minutes, to perform wet-pulverization. Then, the slurrywas batched off and left at rest again, and pH of the supernatantsolution was measured. Then it is found that pH after elapse of 60minutes shows 11.1, and pH after elapse of 120 minutes shows 11.9 andthis reveals that pH gradually rises, along with elapse ofwet-pulverizing time. Then, the value of the pH of the slurry duringthis wet-pulverization becomes higher than pH 8.5 at which Cr isconsidered to be changed to the hexavalent chrome.

When the wet-type pulverization was completed, in the same way as theexample 1, after dewatering and filtering the slurry, decantation wasperformed, thereby drying the sintered powders obtained by cleaning andfiltering, and the strontium ferrite powders with average particle sizediameter of 1.45 μm were obtained.

Next, this strontium ferrite powders were set in the electric furnace,and subjected to annealing for 20 minutes at 980° C., in the atmosphericair, and the ferrite magnetic powders for bond magnet according tocomparative example 2 were manufactured.

When measuring the powder characteristics of the ferrite magneticpowders for bond magnet according to the comparative example 2 in thesame way as the example 1, the specific surface area measured by theair-permeation method was 1.74 μm, and the pressed density was 3.37g/cm³.

Also, the melt flow rate (MFR) was 58.9 g/10 min, being low flowability.

The green compact was manufactured from the ferrite magnetic powders forbond magnet according to the comparative example 2, in the same way asthe example 1. Then, when the magnetic characteristics of this greencompact were measured, Br was 1850 G, and iHc was 2300 Oe.

Further, in the same way as the example 1, the kneaded product accordingto the comparative example 2 was manufactured from the ferrite magneticpowders for bond magnet according to the comparative example 2.

When measuring the magnetic characteristics of the injection molded bodyobtained by injection-molding the kneaded product according to thecomparative example 2 in the magnetic field, Br was 2725 G, iHc was 2463Oe, BHmax was 1.77 MGOe, and SQx was 0.964,

As described above, it was found that the flowabiltiy of the ferritemagnetic powders for bond magnet according to the comparative example 2was deteriorated, thus lowering the SQx value, being one of theindicators in the orientation of the injection molded body according tothe comparative example 2, and the magnetic characteristics seredeteriorated.

Further, when the amount of the hexavalent chrome of the ferritemagnetic powders for bond magnet according to the comparative example 2was measured in the same way as the example 1, it was found that thevalue was 1 ppm or less, being the detection limit or less.

As described above, powder characteristics, flowing characteristics, andmagnetic characteristics were measured for the ferrite magnetic powdersfor bond magnet and the injection molded body according to thecomparative example 2, and measured values of the magneticcharacteristics were described in table 1.

TABLE 1 Ferrite powders for bond magnet Specific surface Pressed GreenInjection molded body area density Hexavalent compact SQx diameter

MFR chrome Br iHc Br iHc BHmax Br/4π (μm) (g/cm³) (g/10 min) (ppm) (G)(Oe) (G) (Oe) (MgOe) Is Example 1.65 3.29 71.5 1≦ 1870 2570 2751 24441.84 0.972 1 Example 1.71 3.31 72.8 1≦ 1870 2560 2757 2440 1.85 0.971 2Example 1.95 3.43 77.8 1≦ 1880 2570 2780 2400 1.84 0.980 3 Example 1.903.41 75.5 1≦ 1880 2550 2760 2433 1.86 0.978 4 Comparative 1.80 3.39 72.349 1870 2560 2753 2442 1.84 0.972 Example 1 Comparative 1.74 3.37 58.91≦ 1850 2300 2725 2463 1.77 0.964 Example 2

indicates data missing or illegible when filed

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a manufacturing example of ferritemagnetic powders for bond magnet according to the present invention.

1. Ferrite magnetic powders, which are the ferrite magnetic powders forbond magnet containing iron and an alkaline earth metal, subjected towet cleaning and/or wet pulverizing process, said ferrite magneticpowders containing a Cr element of 100 ppm or more and 3000 ppm or less,with no hexavalent chrome detected therein.
 2. Ferrite magnetic powders,which are the ferrite magnetic powders for bond magnet containing ironand an alkaline earth metal, subjected to wet cleaning and/or wetpulverizing process, said ferrite magnetic powders containing a Crelement of 100 ppm or more and 3000 ppm or less, with content of ahexavalent chrome set at 1 ppm or less.
 3. The ferrite magnetic powdersaccording to claim 1, wherein in magnetic characteristics of a compactprepared by adding 0.4 cc of polyester resin to 7 g of the ferritemagnetic powders, then filling this mixture into a mold of φ15 mm, andadding pressure of 8 MPa thereto, residual magnetic flux density is 173OGauss or more and intrinsic coercive force iHc is 2270 Oe or more.
 4. Amanufacturing method of ferrite magnetic powders for bond magnet, whichis the manufacturing method of the ferrite magnetic powders formanufacturing the ferrite magnetic powders for bond magnet from rawmaterial powders containing iron and an alkaline earth metal, comprisingthe steps of: obtaining sintered powders by sintering said raw materialpowders; wet-cleaning said sintered powders; and annealing thewet-cleaned sintered powders. wherein in the step of wet-cleaning,cleaning is performed, with pH of a dispersion solvent used in cleaningset at 8.5 or less.
 5. A manufacturing method of ferrite magneticpowders for bond magnet, which is the manufacturing method of ferritemagnetic powders for manufacturing the ferrite magnetic powders for bondmagnet from raw material powders containing iron and alkaline earthmetal, comprising the steps of: obtaining sintered powders by sinteringsaid raw material powders; pulverizing said sintered powders;wet-cleaning the pulverized sintered powders; and annealing saidwet-cleaned sintered powders, wherein in the step of wet-cleaning,cleaning is performed, with pH of a dispersion solvent used in thecleaning set at 8.5 or less.
 6. A manufacturing method of ferritemagnetic powders for bond magnet, which is the manufacturing method offerrite magnetic powders for manufacturing the ferrite magnetic powdersfor bond magnet from raw material powders containing iron and alkalineearth metal, comprising the steps of: obtaining sintered powders bysintering said raw material powders; wet-pulverizing said sinteredpowders; and annealing said wet-pulverized sintered powders, wherein inthe step of wet-pulverization, wet-pulverization is performed, with pHof a dispersion solvent used in the wet-pulverization set at 8.5 orless.
 7. The manufacturing method of the ferrite magnetic powdersaccording to claim 4, wherein carbon and/or a compound having a boilingpoint of 200° C. or more with carbon as an indispensable element and oneor more kinds of elements selected from H, O, N, Cl contained therein,is added to said sintered powders after the step of obtaining thesintered powders and before the step of annealing.
 8. The manufacturingmethod of ferrite magnetic powders for bond magnet according to claim 4,wherein bivalent Fe and/or a compound containing the bivalent Fe isadded to said sintered powders, after the step of obtaining the sinteredpowders and before the step of annealing.
 9. The manufacturing method offerrite magnetic powders for bond magnet according to claim 4, whereinreduction treatment is applied to the sintered powders subjected towet-pulverization and/or wet cleaning in a gas atmosphere in atemperature range from 80° C. to 300° C., containing one or more gassesselected from H₂ gas, CO gas, NO gas, and HC (hydrocarbon) gas.
 10. Abond magnet, containing the ferrite magnetic powders for bond magnetaccording to claim
 1. 11. The ferrite magnetic powders according toclaim 2, wherein in magnetic characteristics of a compact prepared byadding 0.4 cc of polyester resin to 7 g of the ferrite magnetic powders,then filling this mixture into a mold of φ15 mm, and adding pressure of8 MPa thereto, residual magnetic flux density is 173 OGauss or more andintrinsic coercive force iHc is 22700 e or more.
 12. The manufacturingmethod of the ferrite magnetic powders according to claim 5, whereincarbon and/or a compound having a boiling point of 200° C. or more withcarbon as an indispensable element and one or more kinds of elementsselected from H, O, N, Cl contained therein, is added to said sinteredpowders after the step of obtaining the sintered powders and before thestep of annealing.
 13. The manufacturing method of the ferrite magneticpowders according to claim 6, wherein carbon and/or a compound having aboiling point of 200° C. or more with carbon as an indispensable elementand one or more kinds of elements selected from H, O, N, Cl containedtherein, is added to said sintered powders after the step of obtainingthe sintered powders and before the step of annealing.
 14. Themanufacturing method of ferrite magnetic powders for bond magnetaccording to 5, wherein bivalent Fe and/or a compound containing thebivalent Fe is added to said sintered powders, after the step ofobtaining the sintered powders and before the step of annealing.
 15. Themanufacturing method of ferrite magnetic powders for bond magnetaccording to 6, wherein bivalent Fe and/or a compound containing thebivalent Fe is added to said sintered powders, after the step ofobtaining the sintered powders and before the step of annealing.
 16. Themanufacturing method of ferrite magnetic powders for bond magnetaccording to claim 5, wherein reduction treatment is applied to thesintered powders subjected to wet-pulverization and/or wet cleaning in agas atmosphere in a temperature range from 80° C. to 300° C., containingone or more gasses selected from H₂ gas, CO gas, NO gas, and HC(hydrocarbon) gas.
 17. The manufacturing method of ferrite magneticpowders for bond magnet according to claim 6, wherein reductiontreatment is applied to the sintered powders subjected towet-pulverization and/or wet cleaning in a gas atmosphere in atemperature range from 80° C. to 300° C., containing one or more gassesselected from H₂ gas, CO gas, NO gas, and HC (hydrocarbon) gas.
 18. Abond magnet, containing the ferrite magnetic powders for bond magnetaccording to claim
 2. 19. A bond magnet, containing the ferrite magneticpowders for bond magnet according to claim
 3. 20. A bond magnet,containing the ferrite magnetic powders for bond magnet according to 11